The invention relates to a common rail system having a regulated prefeed pump, which pumps a fuel flow from a fuel tank to a high-pressure pump, the fuel flow being split with the aid of a valve assembly into a lubricant flow and a high-pressure feed flow that is pumped, acted upon by high pressure, into a high-pressure reservoir, and the prefeed pump has a substantially linear characteristic feed curve with a certain slope.
To improve the efficiency of common rail systems, it is necessary to establish an equilibrium in the pressure reservoir (rail) between the inflowing and outflowing fuel flow. The attempt is made to do this by on-demand quantity regulation. One such common rail system is described for instance in German Patent Disclosure DE 197 39 653, which had not been published before the priority date of the present application. To keep the lubricant flow constant, a flow regulating valve is used.
The high-pressure pump is driven via the engine. Thus, the rpm of the high-pressure pump is dependent on the engine rpm. In experiments in the context of the present invention, it has been found that the known flow regulating valve, while it does have good regulating performance in the upper rpm range, it does not perform well in the lower rpm range.